What You Need to Know About Vaccines – Part Two

by | Jun 8, 2020


Pharmaceutical companies and researchers around the world are racing to develop a Covid-19 vaccine. As of June 5th 139 vaccines are in development and 18 are in human trials. Part One of this post covered the different types of vaccines and how they work. This post concerns the process for getting a vaccine approved and the success rate of new drugs. This knowledge is important to evaluate the news about new vaccines.

New Drug Approval Process

Vaccines follow the pathway for approval that all drugs in the U.S. go through. Developing a new drug is very expensive and as discussed in the next section below, only a small number of potential drugs make it through the entire process. As noted in a recent article in the New England Journal of Medicine: “Vaccine development is a lengthy, expensive process. Attrition is high, and it typically takes multiple candidates and many years to produce a licensed vaccine.”

Here are the steps for new drug approval in the U.S.:

Source: NEJM

More detail about this process:

PRE-Human Trials:

  • Research and laboratory tests
  • Animal Testing
  • Investigational New Drug application (IND) to the FDA which “describes the vaccine, its method of manufacture, and quality control tests for release. Also included are information about the vaccine’s safety and ability to elicit a protective immune response (immunogenicity) in animal testing, as well as the proposed clinical protocol for studies in humans.” Source: FDA.

Human Trial Phases:

  • Phase One: This phase is focused on the safety of the vaccine, dosage, and whether the vaccine produces an immune response. Phase one trials are usually conducted on a small group of volunteers.
  • Phase Two: This phase is expanded to hundreds of test subjects and is focused on the efficacy of the vaccine.
  • Phase Three: These are typically randomized controlled trials where the vaccine is compared to the efficacy of placebo. This phase is expanded out to thousands of volunteers and usually focuses on high-risk individuals (such as health-care providers).

New Drug Application

If a vaccine passes all three human trial phases the final step is for the drug developer to submit a new drug application. Experts inside and outside the FDA review the application and determine whether to license the new drug.

Here’s a chart from the CDC showing the human trial phases:

Source: CDC.gov

This process takes years. According to the NY Times, “Our record for developing an entirely new vaccine is at least four years.” Most vaccines have taken much longer than that. Here’s a chart from the NY Times:


However, according to explaincovid.org, “in the case of COVID-19, [the usual timelines] are likely to be dramatically accelerated. The FDA is determining which vaccines can go on to clinical trials (without preclinical animal testing) oftentimes based on previous safety and efficacy data of the type of vaccine that is being proposed. Additionally, multiple initiatives, including ones from the Bill & Melinda Gates Foundation and the NIH, have been launched to further speed up development and access to vaccines.”

So, while 12-18 months sounds like a long time, in terms of vaccine development it would be unbelievably fast.

Success Rates for New Drugs and Vaccines

Going from the development phase, through clinical trials and approval is a long, expensive process and most drugs don’t make it through the gauntlet. According to the Biotechnology Innovation Organization (BIO), less than 10% of all new drugs that enter Phase One end up being approved and licensed for use:


The approval rate for vaccines from Phase One to approval is a bit higher than the average for all drugs, coming in at 16.2% according to BIO.

The point of sharing these statistics and the usual timeline for vaccine development isn’t that we won’t have a vaccine, but rather that we shouldn’t just assume we’ll have one in a year. Given the vast number of vaccines in development and entering trials, we can be hopeful, but when we hear of a good phase one result (like with the Moderna vaccine), we should keep it in perspective.

One other hopeful point is that there are 242 therapeutic Covid drugs in development and 154 are in human trials. Many diseases (AIDS being an example) never have a working vaccine but can be managed by therapeutics.

1 Comment

  1. Some say “this time is different” since we have a de facto Manhattan Project at work here…this appears to be a pretty convincing rebuttal to the “typical” vaccine timeline..we shall see…Luv2Nap


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